sheet metal/paint technique question

Most rattle can primers you buy at chain stores are laquer based and are not compatable with urethane or epoxy primers that would be used for the over all paint job. They will soften, bubble and lift if the urethane/epoxy primer is sprayed over them so they will need to be sanded off before final paint adding to the cost.

I recomend you go to any Autobody Supply store and SEM has a line of rattle can primers that are intended for spot repairs and will be compatable with urethane/epoxy primers.

Also, as previously stated primers are porus and if the car is kept outside will not protect it from rusting again unless you use an epoxy primer then it seals.